The fourth outlet of the key and keyup objects output a
keyboard-independent code you can use to detect key presses and releases
as described below.

Letters and Numbers

When pressing a letter or number key,
the values reported from this outlet correspond to the
unshifted Unicode (ASCII) valuversion of the pressed key.

Other Characters

When pressing a key that is a character key but is not a letter or number,
the Unicode value of the key symbol that would be output by the keyboard
when the shift key is not depressed is output.
(For example, on U.S. keyboards,
there is a key with both a single and double quote.
When this key is pressed, the key object will report single quote.

Other Keys

Other keys such as function, home, page up etc. output a consistent values independent of
keyboard on each platform. The values are listed below: